Swift, how to implement Hashable protocol based on object reference?

If you are working with classes and not structs, you can use the ObjectIdentifier struct. Note that you also have to define == for your class in order to conform to Equatable (Hashable requires it). It would look something like this:

class MyClass: Hashable { }

func ==(lhs: MyClass, rhs: MyClass) -> Bool {
    return ObjectIdentifier(lhs) == ObjectIdentifier(rhs)
}

class MyClass: Hashable {
    var hashValue: Int {
        return ObjectIdentifier(self).hashValue
    }
}